The present invention relates to a method for aging a field emission cold cathode, and particularly to a method for aging a field emission cold cathode with a stable electron emission from a cathode.
A typical field emission cold cathode has a structure as illustrated in FIGS. 1 and 2. A field emission cold cathode 10 is formed on an insulating glass substrate 11. A first electrode 12 is made of aluminum and formed on the insulating substrate 11. The first electrode 12 has openings aligned in matrix and each having a small diameter. A resistive layer 13 is formed over the first electrode 12 and within the openings so that the resistive layer 13 is in contact with the insulating substrate 11. The resistive layer 13 is made of silicon. Cone-shaped cathodes 14 are provided on the resistive layer 13 over the openings of the first electrode 12. The cone-shaped cathodes 14 are aligned in matrix. Each the cone-shaped cathode 14 has a top which is pointed and sharpen. Each the cone-shaped cathode 14 is made of a refractory metal such as tungsten and molybdenum. Each the cone-shaped cathode 14 has the bottom having a diameter slightly smaller than "W". A silicon oxide film 16 is formed on the resistive layer 13. The silicon oxide film 16 has cavities 15 each of which is formed to accommodate each the cone-shaped cathode 14. Each of the cavities 15 has a diameter of "W". A second electrode 17 acting as a gate electrode is formed on the silicon oxide film 16. The gate electrode 17 is positioned at the same level as the tops of the cone-shaped cathodes 14. The gate electrode 17 is made of a refractory metal such as tungsten, molybdenum and niobium or rectal compounds.
In the above field emission cold cathode, an electron emission from the top of each the cone-shaped cathode 14 is caused by a potential difference applied between the cone-shaped cathode 14 and the gate electrode 17 without heating the cathodes 14. It is very important that the electron emission from the top of each the cathode 14 is maintained stable. The field emission cold cathode is subjected to an aging process in order to confirm whether each the cone-shaped cathode can maintain a stable electron emission for a predetermined time duration.
As illustrated in FIG. 3, a field emission electron gun 5 is provided with the field emission cold cathode 10, wherein the field emission electron gun 5 is accommodated within a cathode ray tube 1. In the aging process, the field emission cold cathode 10 is accommodated within the cathode ray tube 1. An anode is applied with a-predetermined anode voltage which is lower than the regulated value. The gate electrode 17 is applied with the regulated voltage. The cone-shaped cathode 14 is grounded. A strong field is generated between the top of the cone-shaped cathode 14 and the gate electrode 17.
Immediately after the field emission cold cathode 10 is made, the electron emission from the top of the field emission cold cathode 10 is likely to be unstable. The discharge of the electron from the top of the field emission cold cathode 10 is variable. If in the aging process the regulated voltage is applied to the gate electrode to apply the high field between the cone-shaped cathode and the gate electrode, an excess discharge is likely to be generated between the gate electrode and the top of the cone-shaped cathode. Such excess large electron emission may cause the cone-shaped cathode 14 to be broken.
To settle this problem, it was proposed to provide a convergence and acceleration electrode which is applied with a negative voltage or which is adjusted to be grounded so as to prevent any excess discharge of electrons from the top of the cone-shaped cathode. This field emission electron gun has the additional convergence and acceleration electrode applied with a voltage signal which has to be controlled precisely. The structure and operations of the above device are somewhat complicated. For this reason, it was required to develop a quite novel method for aging the field emission cold cathode included in the electron gun which has the simple structure as illustrated in FIG. 3.